Electrical condenser



July 1-, 1924. 1,499,403

W. H. PRIESS ELECTRICAL CONDENSER Filed Deo. 5 1921' 4 sheets-sheet l i Z5 if .d 4/ if W 75. i i y@ H J if y j? a 57%' ff Z t? y Z 5f h ff www. Z7 ,n In

/s 11i-:11:11, L E 'ffii/f2 "HZ/5;' `\f7 l l ,LT J /f f /f/ /f/ l E! i fr? i ffa/072%?? Q f2 y ///m//f-w July 1 1924. 1,499,403 H. PRIESS I ELECTRICAL CONDENSER FiledDec. .5. 1921 4 Sheets-Sheet 2 w. H. PRl'l-:ss'

ELECTRICAL vCONDENSER l Filed D ec. 5. 1921. 4 sheets-sheet '4 Patented July 1 i 1924.

UNITED STATES `1,499,403 PATENT OFFICE.

WILLIAM H. PRIESS, OF BELMONT, MASSACHUSETTS, ASSIGNOR TC'WIREI'ESS SPllf-A i CIALTY APPARATUS COMPANY, F BOSTON, MASSACHUSETTS, A CORPORATION 0F NEW Yomi.

ELECTRICAL CONDENSER.

Application filed December 5, 1921. Serial No. 519,868.

To all whom it may concern: Be it known that I, WILLIAM H. Pnmss, a citizen of the United States of America, and a resident of Belmont, State of Massa- 5 chusetts, have invented certain new and useful Electrical Condensers, the principles of which are set forth in the following specification and accompanying drawing, which disclose the form of the invention which I 710 now consider to be the bestof the various forms in which the principles ofthe invention may be embodied,

This invention relates to electrical condensers. This application is a continuation in part of m copending application Serial No.' 465,137, led April 2e, 1921. Condensers embodying the present invention are for use generally, but in particular the specic embodiment herein illustratedis adapted for use to interconnect a low loss high-powered radio-frequency reservoir circuit and an antenna circuit tuned tothe same period. The condenser transfers the energy from the reservoir to the antenna. The condenser of this inventionischaracterized by being adapted for high voltages and relatively'small capacity. As an example of a practical and commercial embodiment of such condenser, it may have a capacity of .00002 mfd. and be capable of withstanding 50,000 volts effective, (70,000 volts maximum) at two amperes and 600 meters maximum,

' A feature of the present invention isathat the condenser consists of stacks arranged in series parallel with the casing at the midpoint, connecting the stacks of one set in series with the stacks of the other set.

The type of condenser embodying the 40 present invention is known as a mica condenser inasmuch as it usually comprises a stack composed of alternate sheets of foil and dielectric` the foil consisting preferably of a soft material such as lead or tin, and the dielectric consisting preferabl of mica, which is one of the best dielectrics lmown for this purpose.

The stackseach are made up of sections connected in series with separators between the sections, and are clamped and secured within a suitable casing, the casing preferably in service constituting one of the terminals of the condenser, or an electrical connection between stacks.

Ithas been found that the hysteresis losses in a mica condenser in general increase very rapidly with increased temperature of the mica which results in operating the condenser with the mica at an undesirable point of its phase angle temperature curve. A

stack of a'mica condenser lcomprising theY alternate sheets of foil and dielectric and in a wax filler, or which has been treated with some suitable wax such as paraliin and embedded in such parain, has very low thermal conductivity and thereforeunder load the heat generated is not properly conducted from the stack, which results in high tem# perature rise of the stack. This is further accelerated by the hysteresis losses in mica,

In this invention I increase the heat c`on.

duction and radiation by utilizing in a condenser *of any given electrical characteristics a plurality of stacks each of optimum length for heat conduction instead of a single stack of a length required for a condenser ofv a given voltage and of a given capacity.

' The stack should have a minimum len h for obtaining the maximum heat conductlon and radiation therefrom. This length, however, in a series section stack having ends at a difference of potential should be such that the length of the creepage path between the ends of the stack is adequate for the potential difference to which the stack is to be subjected. In other words, in this design the minimum stack length that can safely be used for creepage for the voltages employed is incorporated in the design. The stack has a maximum thermal conductivity to the casing and to the high potential terminal.

An object of the present invention is to provide a compact, efficient condenser capable of withstanding comparatively high voltages. v

Another object ofthe invention is to provide. a mounting for the condenser having videa compact, eiiicient condenser at rela? tively low cost. 'A

Another object of the invention is to provide' a high potential condenser in which the insulation and heat conduction are handled economically and efficiently.

Another object of the invention is t0 provide a spark-gapl that will ensure proper protection irrespective of careless handling of the condenser.

' sequent destruction thereof.y

Another object of the invention is to pro,

vvide a novel form of spark-gap for preventing excessively high differences of potential between parts of the condenser and the sub.-

Briefly and by way of example, in the embodiment of the invention herein yshown Aand described, I obtain certain of the above objects by providing a condcnserQcasingT having @W0 Chambers, in each of whichfs u stituting a midpoint connection or conducsecured a stack ror stacks, the casingcontor connecting the stacks in the chambers in series andby providing a plurality ot ter- 30 minals projecting thru and insulated trom thecasing. In prior constructions the etfective/voltage seldom exceeded 18.000 .effective or 25.000 volts maximum. The condenser of the present invention is designed 0'/ 35 for 50,000. volts effective (approximately 70,000 volts maximum), The construction above outlined is especially adapted for the voltages of higher ordei` herein specied. If ,only'a single-chambered casing were used and one insulated terminal (as in prior co structions), the insulation of the latter f would have to be extremely large and ex- ,persiva because insulation cost goes up very rapidly ,with increased voltage, much more rapidly than the ratio of increase of voltage. Also the insulation (the filler within t e casing such as wax or oil) between the s aek and a single-chambered casing (which i `at a difference of potential from portions o the stack or stacks) would necessarily VVcdmprise agreater'thickness of iiller to take '/c ie of the greater diierence of potential fbetween" the stack and casing, the dielectric' 'strength ,per unit thickness of insulating .,l .y f material decreasingl with increased voltage (difference. To utilize the designs of prior constructions for the higher voltages here- /jnspeciiied would therefore result irr a very heavy, expensive design or construction.

'Furtherinore, the. large volume of\ filler which' would be necessary in such priorfcon- Y,

stuct'rons to withstand the additionahvoltagesit is desired to handle would 4gr atly reduce the thermal conductivity between the-stacks and the casing, and therefore roduce a very unfavorable electrical loadrating as above explained. I.. have solved the problemv by providing insulators around terminals which are requiredA to withstand'but 'slightly higher voltages than 'previously used and stacks between which andthe cas! ing the insulation is but'slightly..thicker-1l than in forms previouslyldesigned andd from which heat conductionV and radiation is a maximum, yet the whole condenser is so designed as to withstand voltages 'of a comparatii-ely 'higher order such as thoseY above specified.

In the accompanying drawings, I have illustrated one embodiment of the invention Yin which- Figure l is an elevation thereof with part of the casing broken away;

Fig. 2'is a plan view thereof, with part of the casing broken away;

Fig. 3 is a sectional elevation on the line 3-3 of Fig. 2, looking in the direction of the arrows; Y

e Fig4 isan expanded perspective view of a type of stack used in the invention; and Fig. 5 is a plan view of the construction of Fig. 4. i

Referring to the drawings, I have illusltrated a casing 10 containing the condenser elements or stacks SS, which casing is preferably of metal and constitutes a mid-point series connection between the stacks, or, if so desired, a terminal of the condenser. In this embodiment, the casing is divided by a metal conductive partition 11 into two chambers 12 and 13, each adapted to receive a pair of stacks SS", or a two-part stack. The cas ing has an opening at one end, i. e., the bottom, covered by removable closure 14 common to the two chambers l2 and 13 and secured to the casing against a gasket 15 by means of screws 16. At the opposite top end of the condenser casing are openings 17 thru which the high potential terminals and their insulators of the condenser extend, closing the openings as hereinafter described, one of the openings 17 being provided for each chamber, the bottom closure 14, however, being common to both chambers 12 and 13, whereby the latter may be filled with a suit-E able insulating material W such as molten and end to' end within the casing; that is,

the sheets composing themare arranged vertically with reference to closure 14. The inner adjacent ends of the stacks or stack parts engage a suitable metal pressure memsection of each staclyis electrically connected to the y,adjacent pressure plate by means of a copper strip'dead 22 (Fig. 3) which is secured to the free terminal of the outer# i most section andibent backbetween the stack S or S" and the pressure member 20. The inner ends of the stacks are in like manner electrically connected to pressure member 19 by means of flexible copper strip leads 23, which are bent back; an'd interposed between y member 19 and the inner ends of thestacks,

whereby the stacks are electrically connected at their outer ends to the casing as a common conductor, and at their inner ends to' member 19. Each central pressure member v19 is provided with .a threaded opening 24,

in which is threaded a heavy metal rod -or terminal 25, which projects thru the opening 17 to each chamber 12 and 13.

Inasmuch as eachhigh potential terminal 25 must be thoroly insulated from the casing 10, whichv is at an intermediate potential, I utilize an insulating device 26 for each. In the present embodiment, this insulating device comprises a disc or plate27 of insulating material, which is of an area greater than the area of the opening 17in the casing and extending overv the boundaries of said opening. This` disc is preferably of some' material having high insulating qualities and low loss s uch as mica',4 and should be so designed as to withstand the difference in potential between the casing 10 and terminals 25. It is preferred-that the plate 27 consists of mica, which is one of the best materials for this purpose-.the plate being clamped at its edge to the casing 10 by means of a metal ring 28 and screws 29 passing thru the ring 28 into the casing 1 0, a suitable 'gasket 29a being interposed'between the mica sheet and the casing 10 to secure a tight joint. The members 25 extend thru the 'discs 27. Mounted laround each terminal 25 below the plate 27 is an insulating bushing 31 of reduced diameter compared to plate 27. This bushing is provided with corrugations or grooves 33 arranged circumferentially therearound to increase the creepage distance between the terminal 25 and casing 10, and consists preferably ofa laminated structure; for instance, a plurality of mica pieces or discs of diameter sulation varnish or sulfur.

27 and surrounding and insulating the upper portions of the terminal 25. Like the bushing 31, the bushing 32 is also of laminated insulating material preferably built up o'f superimposed pieces or discs of mica and ofA decreasing diameter upwardly as illustrated, forming an upwardly tapering bushing.

The insulating device 26 is preferably constructed or assembled on terminal 25 by assembling thereon thevmica discs, plates or washers in their proper order. In the embodiment herein illustrated, a nut 34 is threaded on member 25. The mica Washers or pieces constitutingthe bushing 3l are then positioned or assembled on member 25 upon nut 34, then disc 27 is positioned and then the pieces .constituting the bushing 32 are positioned on member 25. A round nut 35 is then threaded upon the upper end of member 25 to hold the mica sheets 'and pieces in position against dislocation. The assembly is then treated in a bath of hot molten insulating material, which will act more or less as an adhesive, for about fifteen min-I utes until bubbles cease, either with or without the'appli'cation of vacuum. Suitable materials for this purpose areparaiin, in-

The assembly while hot and impregnated with molten insulating material .is compressed or clamped tightly by nut 35 and allowed to cool, thus clamping the mica sheets together in a solid mass held together by nut 35 (which may be pinned to member 25) and by the fusible insulation which has now solidified. The bushing 32 is then cut, turned or ground to proper shape and polished,l providing a smooth tapered surface. The bushings 31 and 32 are thus retained and supported on plate 27 and held under compression entirely by means of member 25 and nuts 34 and 35. The grooves 33 are formed by assembling intermediate mica washersA of reduced diameter.

Mounted on'each terminal 25 above each nut 35, in close electrical contact therewith and with each member 25, is a concavo# convex metal member 36, having its concave side facing the bushing 32 and having its rounded edge 37 in vertical alinement with and spaced from the clamping ring 28. The inclination of the outer surface of the bushing 32 and the curvature and spacing of the member 36 are so arranged with reference ends of the member 25 produces electrical stresses not thru the insulator 32 but mainly 10, vmaintaining the electrical field thru the air from member.'36 to the casin aralle with the bushing 32 instead of cuttmg the same. In other words, member 36 with casing 10 provides a static shield preventing losses inftheinsulator 32 and theI destruction thereof. The members 36 also perform additional functions in that they provide large-surfaced terminals for radiating heat generated in the stacks and conducted thru the terminals 25 to members 36. The members 36 also serve as protectors or dustguards. for the insulating devices 26, prel venting deterioration thereof; that is, each is located above the insulating disc 27 and ythe bushing 32. Each corona member 36 isl secured in placeA by means of a nut 38' threaded upon the uppenportion of the member 25, and above this are located washers 38a and nuts. 39 whereby any suitable lead may be attached to the high potential terminal in` the usual manner.

The stacks SS in each chamber may be adjusted as a unit by means of the two pressure screws 21, (Fig. 3) in opposite directions to properly'locate each terminal 25 with reference to each other and with reference to its opening 17, whereby the insulating device 26 maybe properly clamped in positin.

It will be "seen that stacks SS of each chamber are connected in parallel with one another, the in-ner or mutually facing ends being connected to the common terminal 25, and their outer ends to the casing, the casing 10 in the present ins/tance forming a midpoint connection between the two sets of stacks in the two chambers.. Casing 10 connects the two sets of stacks in series withthe terminals 25 projecting thru and insulated from the casing. 'f 1 Thus the four stacks are connected in sej ries parallel between the two condenser terminals 25. The circuit is from one terminal 25 to central pressure member 19 in one chamber of the casing, thence in parallel through the two stacks in that chamber abutting said member 19,'thence to casf ing 10, thence tothe'outer ends of the two stacks in the other/casing-chamber, through l said latter stacks inparallel to their central abutting member 19 and thence to the other condenser terminal 25.

`In order to protect the condenser against excessively high voltages, beyond a value for which the condenser is designed, I have provided a spark-gap device (Fig. l) which co` /operates with each of the shields 36 to form therewith spark-gaps. This Aspark-gap device comprises a metal rod or stud 40 threaded into the to of the condenser casing 10, in conductive re ation thereto (i. e., connected to the midp/oint of the condenser between the two sets o, stacks) vand between and in fspaced relation to. shields 36 of the two, tering on conditions.

minals 25 from the sets-of stacks. The upper en d 41a of the irpetal rod 40 is threaded. Meshing with the threaded end 41x1 is an adjustable conical metal member 42, which may be adjusted vertically to vary the distances between its inclinedr surface 43 and the adjacent shields 36, providing with shields 36 spark-gaps for protecting each set of stacks SS', the length of the gaps depend- The conical member 42 may be locked by a set screw 41 after its correct location is determined for any given condenser.

The distance between members 42 and 36\ to form a spark-gap depends on the radius of curvature of adjacent portions of thel two parts, the shorter the radius of curvature of such adjacent portions the greater the distance or spacing betweenvthem must beto withstand a given dierence of potential. In the present design, the distance between the member 42 and each edge 37 of each bell 36 is such as to provide the required spacing to protect the condenser for the given radii of curvature of such adjacent parts, the greater the radius of curvature of such adjacent portions the less the corona effect between the parts at a difference of potential will be and the less the distance may be to protect each set of stacks from voltages exceedingl the designed value. v

vThe object of the spark-gap device ofthe present invention is to protect the condenser by preventing the user from exceeding the rated potential. Axial adjustment of conical member`42 sets a protection of equal value for each fhalf of the condenser. If member 42 is removed from stud 40, for any reason, the spark-gaps consist of stud 40 and the shields 36. The threads on stud 40 have a very small radius of 'curvature so that when member 42 is removed, the condenser will spark even at a potential lower` than the rated voltage or lower than the voltage each set ofv stacksiis designed to stand even tho the length of each gap is thereby increased. If stud 40 also is removed, there will be formed a single spark-gap between the two shields 36 protecting both sets of stacks against voltages exceeding those for which the condenser is designed, Inlike manner, when the two shields 36 constitute the spaced members of the spark-gap, the condenser will spark over at a'potential lower than the total rated voltage, the radii of curvature of 120 effective from either shield 36% the memlao ber 42. With member 42 removed, the iistance between each shield 36 and stud 40 is increased to about "78 inch, but owing to,

the small radius of curvature of stud or its threads compared to that of member 42, the condenser will {iash over around 24,000 or 25,000 from either shield 36 to the stud 40, still maintaining the rotection below the designed value. If stu 40 is removed', the distance between `the two shields is about two inches, butin this case the gap must handle the entire voltage impressed across terminals 25' and with a given radius of curvature of the edges 37, the condenser will spark over at about 46,000 volts effective.

When stud 40 is removed, the gap formed by the two shields 36 will not protect the condenser in every case because of the conditions existing in the circuit in which the condenser is used. In most cases, however, when the stud 40 and member 42 have been removed, probabythru carelessness, the gap between the shields will be sufficient to protect --the condenser. The spark-gap device above described and herein illustrated is yfool-proof. The adjustability of member 42 is a convenience in securin the correct spacing between member 42 an each shield as the members 40-42 are in electrical conl nection to -the casing 10, (a midpoint series connection between thetwo sets of stacks,) each ga formed between them and one of "the shie ds 36, controls only approximately one-half of the total impressed voltage. But

when the two shields 36 form the gap, this gap protects the condenser against voltages the total designed voltage, altho greater than twice the distance between each gap and conical member,'42. Inasmuch as the potential necessary to break down a gap does notvary as a straight line function of the len th of the gap, the longer gap will break own at a potential'lower' than twice the potential necessary to break down one of the shorter gaps.

The construction of the present invention issuch that the stacks are securely clamped within the casing and with the terminals and leads thoroly insulated from the casing 'and from each other. The arrangement of stacks vprovides a condenser capable of withstanding a high voltage; for example, of the order of 50,000 volts eifective and 70,000 volts maximum. At the same time, the condenser may be of any capacity, even of a very low order.

The arrangement of spaced terminals 25 upon the top of the condenser and the electrical connection between the stacks and the casing 10 allow the use of three diii'erentl values of capacity in the condenser by- (l) Employing the two terminals 25 as the circuit connections, in which case the' circuit will be as above described in detail.

(2) Employingfone of the terminals 25 and the casing 1 0 as the circuit connections, in which case the two stacks in only one chamber will be in circuit, being in parallel with one another.

(3) Employing both of the terminals 25 parallel connected together as one terminal and the casing 10 as the second terminal, in which case all four stacks will Vbe in parallel with one another.

It is preferable that the two oups or sets of stacks or elements be of equa capacity so that when used in series, the potential across each stack will be the same. groups were of unequal capacities, the potentials `would divide inversely as` the capacities and the sections of the group of smaller capacity would receive a disproportionately greater strain than the sections of the group of larger capacity. Whenl the groups arev connected in series, twice the potential that can be a plied to a sin le group may be applied to tihe condenser. e

lthe capacity of one of the grou s of elements. When the condenseris use with one terminal 25 land the casin as the connections, the potential of a slngle group can be applied to the condenser and the capacity v will be the capacity of a single'group of sections. When both terminals 25 are connected and form one of the terminals of the condenser, the potential of a single grou may be impressed across the condenser an the capacity ofthe condenser will be twice the capacity of one of the groups. If the capacity of each group is taken -asv unity, then the capacity of the'first grouping lwill be one-half, of the second grouping, one, and

of the third grouping, two, respectively. Inasmuch as the stacks SS of the present invention are composed vof sections confmA 'capacity of the condenser will then be half msv nected in series, in service there will be a fall of potential from one end of each stack to the other. In this embodiment ot the invention, the stacks of each set are arranged substantially parallel to each other, one set in each chamber, the sets being separated from one another by metal wall 11 (Figs. 1 and 2) which receives any heat conducted thru the filler W from the stacks on oppo-f site sides of it. The metal casing, (to reduce the size of' the condenser, increase its heat conducting properties, and lower its cost,) is as closerto the stacks at all points, consistentwith good insulation as possible. The outer ends of the stacks S are electrically and thermally connected to the casing and hence at the same potential therewith.

g f l' 1,499,453

VAt points on tlhe stack at substantially the. or other similar material. Folded over op- -potential of the casing (as at theends), the posite faces of each separator is a foil sheet casing may be located close to the stacks 58 forming conducting sheets on opposite with increasing separation between them as sides of the separator connected by an intetheA potential difference increases as indigral connection 59, the parts of the foil 58 cated at 44, Fig. 2. The portions 44 of the vupon opposite sides of the separator being casing walls f'between the parallel sets of spaced \inwardly from three edges thereof` stacks therefore converge towards each forming margins 60. The sheets. 58 may other, forming angular spaces 45 between -be very, easily folded around/the separathem, the walls of which may merge with partition 11. y centeringV the foil on each separator. The

The condenser herein described may be separators 57 are -arranged in /superimmounted in any suitable manner, but in theVr posed position to form a stack zith dipresent construction, sincethe casing is VYafrrelectric sheets 61 vbetween opposing conmidpoint series connection between the two ducting sheets 58 of successive separators, groups of stacks and hence at an4 interthis dielectric being preferably a goodlqiualmediate potential, I utilize an insulating ity of mica. The separators 57 arer armounting as illustrated in Figs. 1 and 3.V ranged in the stack as to position thelcon- As illustrated, there isprovided a tubular-"nections 59 alternately at opposite'fsides. mountin 46, suitably supported, on which The-dielectricsheets 61, which are of subis secure one or more insulators 47 by means stantially the same'area as the separators i of a two-part metal clamp 48, one part 49v 57, are slightly offset, relatively to the sepabeing secured to the insulator 47 and the rators, alternately at opposite sides as indiother part 50- securing the insulator to Y cated at 62 (Fig- 5) in order better to inmounting 46 by means of screws 51. Upon sulate from each other successive connections the opposite end of the insulator 47 is se: 59 at succeively alternating sides of the cured a metal cap 52. The cover 14 of eachLstack. Each dielectric 61 with the foil condenser is provided with lugs 53 (Fig. 3) sheets on opposite sides thereof forms one arrangedl on a line centrally thereof and to section of the stack, the severalsections bewhich is secured by means of screws 54 a 'ing connected in series via the alternate intemetal cross bar 55. The-condenser is supgral' connections 59. rlhe construction above ported centrally oninsulator 47 by means of described is of distinct advantage in being tors with their ends in line, thusproperly screws 56 projecting centrally thru bar 55 easy to assemble at low cost, and if of speciak into cap 52. The condenser is thus supadvantage where astack of lowcapacity and mgproper-ly balanced thereon. Y as the casing is at a midpoint potential, the of foil conductors and a single intermediatel amount of insulation necessary at 47 in the` diefefctric 61', each foil sheet engaging-ase'pageneral case is only about one-half of that rato'r 57 and bent around the edge thereof. which would be necessary if the casing'were one of the terminals of the condenser. either as illustrated1inr Figs, 43 or. 4, may i In Figs. 4 and 5, I have illustrated a form be constructed and assembled im part in the v,of stack` which I prefer for use in the form manner described in my 'copending applicaof condenser herein illustrated, altho the tion Serial 1`Tol' 456,903, liled-/March 30 stack therein illustrated is of general appli- 1921. The 'rocess therein described covers cation. The showing in Fig. 4 is an ex- Vthe manufacture of a stack by preliminary panded view; that is, the several parts of dipping the individual sheets of mica in the -stack are shown separated for purposes suitable insulatinv material, such as molten of convenience to more readily illustrate the paraliin, and building what is called the construction of the stack and the methodA of Vmaterial stack consisting of alternatesheets building the same. When assembled in the of foil and dielectric, and then 'treating the condenser, the several parts are 'inf contact, material stack thus .formed in molten insu- Abeing suitably clamped'togetherto form alating material such asparatn and applysolid stack (either with or without impreg- 'ing high compression and cooling, forming a nating material adherlngthereto as desired solid block. After this, as in the forin'illusor according to conditions), the clamping trated in Fig. 3, the material stack is split means being such as disclosed in'Fig. 2, the up into sections, which are connected in stacks SS illustrated therein 'being conseries `and the insulating separators between sidered stacksnfthetype shown `in Figs. 4 the sections inserted. 'Of course, the sections and 5, if s0 l may be assembled and connected by any de- My limprove/d stack comprises several insired method, such asy that illustrated in Sula-ting separators 57 which may consist of Fig. 4. Or, for instance, each vsection mayv are not subject to dielectric strain) micanite section is then tested for capacity and voltseveral layers of mica (preferably cheap der,- oe built 11p under molten waX, heated, comfective mica, inasmuch as such separators pressed and cooled under pressure. Each The stacks SSof the present invention,l

s sico orted centrally upon a single insulator,.be relatively high voltage is required as in F igs Inas'mucli `1-3,fs,ince each section comprises two she\ets\- Aage. The sections are then connected in series and separators inserted between them.

l After the sections have been' connected by to receive the corners of the condenser stacks."

or,l if so desired, a stand having six rods may be used, two rods engagin each side of the stack and one at each en v. A stand adaptable for this urpose is disclosed in a pending application of G. W. Pickard, Serial No. 380,919, filed May 12, 1920. The stack when positioned in the stand is su ported and braced by the vertical ro s against dislocation and side slip. The stack and stand are then placed in a hot molten paraiiin bath or a bath of other insulating material for a proximately twenty minutes until the stadlr is warm, the bath being at approximately a temperature of 130o C. The stack and stand are then removed from the bath, and the stack while still Vin the stand and while still hot, is placed underya pressure ofthe order of magnitude of a ton per square inch over the active surface of the stack, and allowed to cool under pressure before bein placed in casing 10, `the vertical rods o the stand su portin and bracingthe stack against e he stack while under thepressure of the order of I magnitude `above-*mentioned and after cooling is tested for capacity, and the capacity finally adjusted to its correct value, if this is necessary. Thus it will beseen that the final and correct capacity can be obt ktained before the stack is finally clamped in the casing 10 and embedded, thereby avoiding the removal of the filler after finally embedding for the purpose of obtaining the desired capacity, vif on test the capacity is found to be wrong.' -By cooling the stack under pressure outside of the v casing in the manner above-described, the stack can also be tested for breakdown before being placed'in the casin as well as' measured for final length. urthermore, by thus waxing and cooling the complete condenser stack, including the separators between sections, before being placed in the casing, it can be handled, asa block`and side -slip cannot occur during the filling operation after the stack SS i's placed within the casing 10 and maintainedunder pres-v sure by pressure members 20 and screws 21.

In former processes and methods of building stacks and assembling them within the `condenser casin the wax treatin compression and coo ing operations on t e completed stack, including the separators in "secured within the casing 10 b the clamping members 20 an place, as well as the final adjustment of capacity, usuallyhave been done in a permanent clamp forming part of the condenser and in the condenser casing. In that process, however, it was diiiicult to maintain( good stacks where the length of the stack exceededv by over twice Ithe largest `dimension 'of the base or where sectional sion, the elements of the stack tended to be displaced relatively to each other. By providing lateral support for the stack during compression, this diiiiculty is obviated.

After the stacks SS', including the separators,'have been waxed and compressed,

cooled yand tested as above described, they are in condition to be handled, being cold and covered with wax, and are directly means of screws 21 'in the manner abo've described (Fig. -The terminal gaskets 29a are then positioned (Fig. 1) and terminals 25 threaded into block 19 (Fig. 3). vThe insulators 26, around terminals'25 (Fig. 1), including the discs 27, are then clamped to the casing by means of rings 28 and scre s 29. The bells 36 and remaining nuts a e then assembled and spark-gap device 42 properly located.

After all the parts have been assembled as illustrated in the drawings, with stacks SS held under'sufiicient pressure to hold them in place, the whole condenser can be inverted, the'bottom` 14 being removed, and casing 10 filledv with insulating material W, preferably molten paraffin or oil, in the manner described in my application 456,903 above-mentioned to provide a compact, non-porous, holosteric embedment W for the stacks and around the bushings and terminals within the casing l10, which is free from air and voids. As described in such application 456,903, a head or extension is secured to the' casing and the casing and extension are preliminarily heated by filling the same with molten paraiiin' at a temperature around 140 C. While thus filled, the final pressure is applied to stacks SS by tightening up screws 21. moved and vacuum applied and the casing and extension filled with molten paraffin or other insulating-filler, whichis allowed to solidify from the bottom upwardly inthe manner described in said application 456,903. In some cases, the preliminary heating with paraliin may be omitted and the stacks SS finally clamped under high pressure as soon adjusting The molten paraffin is then reas positioned. The condenser vstacks and terminals are then embedded, and the head and surpluswax or insulating materialA removed as described in said application 456,903.- .After the embedment, the bottom 14 with its intervening gasket l5, is secured in placey by means of the screws 16.

The insulators 26', for the purpose of insulating the highpotential terminals 25 from' the casing, providea long creepage path with short height. Additional creepage is .ob-

y tained by providingA circumferential grooves in either or both of the mica bushings upon either or both sides of the mica discs 27. I have shown such grooves 33 in the mica bushing 31. In the present construction, each insulator 26 comprises a single mica disc27 clamped to the casing 10, and built-up discs of mica of reduced diameter` forming bushings upon and supported by the disc 27, the bushings being clamped to theldisc v27 at opposite sides thereof by means of the member 25 and co-operating nuts threadedV thereon.

By the present invention, instead of using one stack, I have used four stacks, each stack.

having a minimum length consistent with the creepage requirement between the opposite ends of the stack duc to voltage differences.

Each stack has maximum thermal conductivity to the casing and to the high potential terminals. Each high lpotential terminal is provided on the exterior-of the condenser with a corona spark-gap shield constituting a heat-'radiating member, the casing 1() constituting the other heat-radiating member. It will thus be seen that each stack, of minimumlength, engages at opposite ends conductors having a high thermal conduc- -tivity and large heat-radiating powers. The

above-described is such that the stacks aremaintained at a minimum vtemperature for a given load, which results 1n efficient operation and low loss. In this inventionybyl placing fourl short stacks, which are electrically in seriesparallel with one another and each consisting of series sections, thermally parallel between high-conducting terminals,

'the thermal path is improved in a ratio of approximately sixteen to one over a single stack having the same electrical character# l istics. vIn this arrangement, I have improved the condenser construction so that it will carry four times the energ fof the equivalent single stack with the same eating. In the present invention, `alsoy for?) the same capacity', I have been able to yreduce the amount of mica required in a condenser, thus materially reducing thelcost. For instance, in a condenser having a single stack of the same length as thetotal length of the four stacks of the present condenser and having the capacity of the condenser of the present invention, there would be required mica sheets of four` times the area over those required forth'e condenser of this invention. Furthermore, a much more expensive clamping means would be required to obtain the same pressure per unitarea, this clamping means moreover would be inferior and inefcient as well as bulky.l In the present invention, by the methods of manufacturing the stack as above-described, and by reason of thel minimumlength of the stack, side slip has been reduced to a clamping feature simpliiied while maintainin@ the high pressure.

- t will be seen, therefore, that the present invention provides a very eflicient high tension condenser which is very compact, in which the stacks are maintained under the highest practicable compression to maintain the sheets of foil and dielectric. in intimate contact to prevent losses in the stack and to increase its thermal conductivity. The casing forms a heat-conducting and radiating device in cont-act with the outer ends of the stacks. `Theinner ends of the stacks, in like manner, have high thermal conducminimum, and the ,tivity to the'outside thru blocks 19 and terminals 25, where the heat is radiatedby the heat-radiating members 36 upon the termi nals.

nv is t@ be understood that the invenu0n is not limited to the embodiments and features specifically shown and described herein, but that such embodiments and features are 'subject to. changes' and modifications without any departure from the spirit of the invention.

I claim y 1. An electrical condenser comprising a plurality of stacks of sheets, a common metal casing for said plurality'of stacks by vwhich casing said stacksiare connected inl series; and a 'corresponding number ofcoudenser lterminals extending from the stacks through the casing and 'insulated ,therefrom. 1

2. In an electricalcondenser, a-metal casing, terminals projecting thru said Casin and insulated therefrom and a luralityio sets of condenser stacks mounted? in the casing with the' stacks of each'set electrically connected in parallel between the casing and one ottheterminals, thesets of stacks beingv electrically connected by said casing.

3. In an electrical condenser, a metal. casing, terminals projecting thru said casing and insulated therefrom,ra plurality of -sets of condenser stacks mountedyin the casing' with the stacksof each s et electrically iconnected in parallel between the casing and one of the terminals, each stack' comprising a-number of sections connected in series, the

lsets of stacks being electrically connected in 'series by` said casing.

4. In an electrical condenser, a lurality of stacks, a metal clamping mem er sur rounding said stacks and electrically connecting them'in series and terminals' electrically connected to said'stack's.

5. AIn an electrical condenser, al plurality trically connecting them in series at adjacent ends thereof and terminals electrically connected to the oppositeends of the stacks.

6. In an electrical condenser, a plurality of sets of stacks, each stack comprising sections connected in series, a met-al clamping member surrounding said stacks, and terminals electrically connected to the. stacks, the stacks of each set being electrically connected in parallel between said clampin member and one terminal and the sets being electricallyconnected in series by said clam ing member. v

7. In an electrical condenser, a metal casing havinga plurality of chambers, condenser stacks mounted in the chambers and electrically vconnected together thru said casing and terminals projecting thru said casing and insulated therefrom and electrically connected to said stacks. 8. In an electrical condenser, a. metal casing having a plurality of chambers, terminals ro'ectino thru said casing at one side P e e and insulated therefrom, a removable closure for an opening in the casing at a side thereof remote from the terminals, said closure being common to the two chambers', a plurality of stacks of short length for heat conduction as compared with a' single stack electrically equivalent to the plurality of stacks and mounted Within the chambers and electrically connected to said casing and terminals and a filler of insulating material within the casing and surrounding the stacks and terminals and placeC therein thru said opening.

9. In an electrical condenser, a metal member, a plurality of stacks mounted Within said metal member out of alinement with each other, said member constituting a common electrical connection between the stacks and means electrically connected to the stacks and insulated from said member. for completing the circuit of said condenser.

l0. In an electrical condenser, a metal casing, spaced terminals mounted on said casing and insulated therefrom and pairs of stacks'arranged side by side within the casing and clamped therein, said stacks coinprising series sections and having their outer ends electrically connected to the casing as a common conductor, said terminals being electrically connected to the intermediate portions of thepairs` of stacks.

.11. In an-y electrical condenser, a metal casing, a plurality of sets of stacks mounted .within the casing, -each stack comprising a number of sections connected in series and composed of foil and dielectric and the stacks of'each set being arranged end toend and horizontally within the casing, a central metal pressure member arranged between the inner adjacent ends of the stacks of each set, pressure members engaging the outer ends of said stacks, screws threaded in the casing and engaging saidouter pressure members for clamping each set of stacks and supporting them from the casing, terminals 'engaging in said central pressure members and projecting thru the casing, insulating bushings mounted on said casing and surrounding said terminals for insulating the latter from the casing, metal 'members mounted on said terminals above said bushn ings for preventing loss in thefy bushings and for heat radiation, the stacks of each setr being electrically connected in parallel between tlie casing and one terminal and the sets of stacks being electrically connected in series by said casing, and a filler of insulating material surrounding said stacks Within the casing. i

l2. In an electrical condenser, a metal casing having two chambers, a pair of condenser stacks mounted in each chamber,

pressure members, with Which theiniier ends K of the stacks of each pair engage, and adjustable devices threaded thru the 'casing and engaging the outer ends of the stacks for supporting and clamping them in position, said stacks being electrically connected to said pressure members and to the casing, and terminals connected to said lmembers and projecting thru the casing and insulated y 14. In an electrical condenser, a metal casing having a metal partition therein form ing chambers upon opposite sides thereof and condenser elements mounted in each chamber, said casing and partition conducting and radiating heat from said elements.

15. In an electrical condenser, a metal casing having a partition therein dividing the casing into chambers, stacks mounted in the casing in said chambers and connected to- 'gether electrically thru said casing, and insulated terminals connected to the staclrs and projecting thru the casing from said chambers.

lAn electrical condenser comprising a metal casing, a plurality of short stacks of sheets therein; a corresponding plurality of vradiators outside said casing; a correspondpair having a heat-absorbing member located between the adjacent ends; a plurality of heat-radiating means ocated outside said casing; and a corresponding plurality of heat-conducting condenser-connections extending from said respective heat-absorbing members; through but insulated from said casing, and to said heat-radiating fmeans, re-

spectively; the outer ends of said double stacks being in good thermal and electrical cnducting relation with said metal casing.

18. An. electrical condenser comprising la plurality of double stacks and a metalv casing therefor; and a corresponding plurality of condenser-connections extending from the ,midpoints of said respective double stacks vand through but insulated from said casing;

the outer ends ofsaid double stacks being. electrically connected to said metal casing, and the half-stacks being short in length as compared with a single stack electrically equivalent with the pl-urality of stacks.

19. An electrical condenser comprising a plurality of stacks of sheets; a metal casing therefor; heat-absorbing members located respectively in and intermediate the ends of eachstack, thereby c onstituting'it a double stack by dividing it into tivo sections short in length as compared with asiugle stack electrically equivalent to the plurality of stacks; two heat-absorbing metal clamping members engaging the two ends of each doublestack; a plurality of radiating members located outside the casing and electrically insulated therefrom; a plurality of heat-conducting condensenconnections extending between said intermediate heat-absorbing members and said external radiators,` and' insulated, from said casing; and clamping screws traversing the casingoualls,r engaging said clamping members, and electrically connecting the ends of the double stacks with the metal casing.

20. An electrical condenser comprising a plurality of stacks of sheets; a metal casing formed with a number of chambers corresponding with the number of stacks, the stacks being located insaid chambers and having their outer ends electrically and thermally connected to the casing; heat-radiating means vlocated outside said casing and electrically insulated therefrom; and heatthe ends of each stack being electrically connected to the metal casing whereby the latter is at a potential intermediate that of said circuit terminals; and an insulating support secured to said casing.

22. fin electrical condenser comprising a plurality of stacks of sheets each of which stacks is short for heat-conducting as compared with a single stack equivalent to the plurality of stacks; a metal casing enclosing said staclsand formed with a plurality of chambers; said stacks being arranged in pairs end to end, a pair in each casing` chamber, and the pair in Aone chamber being located substantially parallel to the pair in another chamber; the ends of the pairs being in good electricalv and thermal connection with the'casing as a heat radiator; a plurality of radiators mounted on and insulated from the casing; and the adjacent ends of the pairs of short stacks being in good thermal and electrical connection with said external radiators.

WLLIAM H. PRIESS. 

